MULTIWAVELENGTH MOLECULAR FLUORESCENCE SPECTROMETRY FOR QUANTITATIVE CHARACTERIZATION OF COPPER(II) AND ALUMINUM(III) COMPLEXATION BY DISSOLVED ORGANIC-MATTER

Conditional stability constants and binding capacities are important p arameters with which to estimate the biological availability of metal ions in aqueous solution in the presence of dissolved natural organic matter (fulvic acid, organic matter in natural waters or in aqueous ex tracts of forest litter). Determination of these parameters depends on analytical methods that can distinguish between free and organically bound metal ions. This speciation is difficult, mainly because natural organic matter typically is a complex mixture. In this paper, multi-w avelength molecular fluorescence spectrometry is evaluated prototypica lly as a method for the determination of stability constants and bindi ng capacities for Cu(II) and Al(III) complexation by dissolved organic matter in a juniper leaf litter extract. Equilibrium ion exchange qua ntitation and electron spin resonance spectroscopy served as quantitat ive and qualitative reference methods, respectively. Three types of bi nding site for Cu and Al could be differentiated qualitatively by the reaction patterns of various wavelength regions of the total luminesce nce spectrum of the leaf litter extract in response to increasing meta l ion addition. For both Cu (pH 6) and Al (pH 5), binding parameters f or the two types of binding site forming the most stable complexes wer e deduced self-consistently from reactions evaluated at selected excit ation/emission wavelength pairs.